Hot-melt adhesives are generally processed in the molten or liquid state and acquire their adhesive properties on cooling, while becoming solid.
Crosslinkable hot-melt adhesives, in particular those containing isocyanate groups, are widely employed for assembling various materials such as wood, plastic, paper or cardboard because of their mechanical strength and their great heat stability.
Such properties are essentially due to the fact that, after the adhesive bonding, the reactive groups in the adhesive crosslink by reacting with water.
The abovementioned compositions, which are described as reactive, must be preserved from any premature crosslinking, in order that they may retain good performance and good homogeneity at the time of the adhesive bonding.
To this end it has been proposed to package such reactive hot-melt adhesives in the following packagings:
The most widely used packaging consists of a simple container inside which a flexible barrier film is placed, in most cases in the form of a bag, it being possible for the said container optionally to comprise a lid provided with a waterproof seal.
In EP-A-661 221 it is proposed to pour the adhesive into a primary container made of rigid material, the latter being placed in a secondary container substantially identical with the first in size and shape. The free surface of the adhesive is coated with a flexible film which has a low permeability to water vapour and the whole is closed with a sealed lid.
In EP-A-469 564 and EP-A-649 718 it is proposed to package one or more portions of adhesive in an enclosure which is flexible and compatible during the melting, and to place the whole thus formed in a second packaging, for example an enclosure or a container.
However, the packagings just described have disadvantages.
The abovementioned first two packagings require the transfer of the adhesive into the applicator device, and this is generally carried out by means of a hot plate. With the first container there is a risk that the inner film may tear or that it may not be possible to recover all of the adhesive, because of the folds in the film which are formed at the time the container is being filled.
The last packaging mentioned, for its part, requires the use of a stage of forming and conditioning of the portion(s) of adhesive, and this is relatively more complex and costly than a simple dispensing in the molten state.